Tsunami

The phenomenon called "tsunami" is a series of ocean waves of extremely long length generated by undersea earthquakes, volcanic eruptions, or massive undersea landslides. As a tsunami crosses the deep ocean its length from crest to crest may be a hundred miles and its height from trough to crest only a few feet. Tsunamis may reach speeds of 600 miles per hour in deep water. When the tsunami enters shallow coastal waters, its speed decreases and the wave height increases. This creates the large wave that becomes a threat to lives and property. Following the arrival of the first wave, subsequent waves may increase in height and arrive minutes to hours later. The 2004 Indonesian Tsunami caused over 300,000 deaths.

Although there are no known recorded deaths from tsunami action in Marin County, there were small tsunami impacts in 1946 and 1960. In 1964, the Alaskan earthquake damaged buildings, docks, and boats in Sausalito and San Rafael.

The County of Marin has produced Tsunami Evacuation Planning Maps for the Pacific Coast areas. The maps are intended to support evacuation planning purposes only and do not necessarily reflect how a tsunami wave may actually impact the mapped areas.

Residents and visitors to coastal areas must be aware that there may not be time or means to provide any warning of a tsunami threat. An earthquake felt along the coastline is a signal to move immediately to higher ground. This must be done if there is no information or any formal tsunami warning issued. Any associated earthquake could also damage structures and infrastructure in the potential inundation Area prior to the wave’s arrival. This could significantly impact warning, evacuation and emergency response operations.